1. Field of Invention
The present invention relates to a saw for cutting concrete, asphalt, and other hard, flat surfaces and, more particularly, to a self-propelled concrete saw equipped with a forward motion speed control system.
2. Description of Related Art
Large, horizontal slabs of concrete are frequently poured during the construction of buildings, bridges, roads, runways and the like. Once poured, such slabs must often be cut or scored using a concrete saw for various reasons such as, for example, to form expansion joints, to allow for foundation shifting, to create stress cracks along which the slab will split and/or to create high friction surfaces such as for bridge decks and airport runways. In most large-scale applications, a self-propelled concrete saw is used to cut or score the slab. Self-propelled concrete saws are also used to cut or score asphalt, stone and other hard surfaces.
Most self-propelled concrete saws are equipped with a power plant (e.g., an internal combustion engine or electric motor) and a drive system that is configured to rotate a diamond impregnated saw blade during the cutting and/or scoring operation. The power plant is usually configured to produce maximum horsepower in a peak operational range, which is usually expressed in terms of a range of revolutions per minute (“RPM”). In this peak operational range, the power plant can generate maximum torque, and thus the work the saw blade can accomplish is also maximized. Internal combustion engines, in particular, are usually designed to provide maximum engine cooling in this peak operational range.
Diamond impregnated saw blades are extremely durable, but they do wear out over time. Studies have shown that the service life of a diamond impregnated saw blade is maximized when the blade is rotated at a rate within a specified range of optimal angular velocities and when the torque loading on the blade is held within a specified range. Excessive angular velocities or torque loadings can result in premature wearing, while insufficient angular velocities or torque loadings can cause the cutting surfaces of the saw blade to become polished, which severely diminishes the cutting efficiency of the saw blade.
Generally speaking, torque loading on a saw blade mounted on a self-propelled concrete saw is a function of the depth of cut, the rotational energy being transmitted to the saw blade by the power plant, and the forward motion speed of the concrete saw. The depth of the cut is usually application specific, and thus cannot be varied to optimize the speed of the cutting or scoring operation and/or the service life of the saw blade. The power plant is configured to operate in a peak range or band of optimal RPM's, and thus it is generally not advantageous to attempt to adjust the rotational speed of the power plant to optimize the speed of the cutting or scoring operation and/or the service life of the saw blade.
In most conventional self-propelled concrete saws, the forward motion speed of the concrete saw is set at a constant predetermined speed, or is manually controlled by the operator of the concrete saw, who walks behind the saw making adjustments in response to perceived changes in the performance of the concrete saw. In either instance, an operator must manually select and control the forward motion speed of the self-propelled concrete saw in response to perceived torque loading on the saw blade in order to attempt to maintain the angular velocity of the blade and the torque loading on the blade within their optimal ranges. This requires a high level of operator skill and creates a risk that the operator will select a forward travel speed that will damage the blades.